1. Field of the Invention
The present invention relates generally to verification, authentication or identification systems, methods and program products, and more particularly, it relates to inserting and detecting identifying data artifacts within lossy and lossless transmitted data.
2. Description of the Related Art
Systems for identifying, verifying, or authenticating transmitted data are known in the art. Such systems allow a transmitted data signal, also known as carrier data, to be marked with a verification code sequence identifying the owner, time of production, title, or other suitable data. The verification code sequence is used to identify the carrier data so as to verify performance of the carrier data, determine the source of the carrier data, or perform other suitable functions.
Various prior art methods of injecting additional information onto carrier data sequences are known. For example, the time domain may be used for digital information injection. It is known to pulse-width modulate a signal to provide a common or encoded signal carrying at least two information elements or other useful elements. In U.S. Pat. No. 4,497,060 to Yang (1985) binary data is transmitted as a signal having two differing pulse-widths to represent logical “0” and “1” (e.g., the pulse-width durations for a “1” are twice the duration for a “0”). This correspondence also enables the determination of a clocking signal.
Other examples use the frequency domain for digital information injection. U.S. Pat. Nos. 4,876,617 to Best et al. (1989) and 5,113,437 to Best et al. (1992) disclose encoders for forming relatively thin and shallow (e.g., 150 Hz wide and 50 dB deep) notches in mid-range frequencies of an audio signal. The earlier of these patents discloses paired notch filters centered about the 2883 Hz and 3417 Hz frequencies; the later patent discloses notch filters but with randomly varying frequency pairs to discourage erasure or inhibit filtering of the information added to the notches. The encoders then add digital information in the form of signals in the lower frequency indicating a “0” and in the higher frequency a “1”. In the later Best et al. patent an encoder samples the audio signal, delays the signal while calculating the signal level, and determines during the delay whether or not to add the data signal and, if so, at what signal level. The later Best et al. patent also notes that the “pseudo-random manner” in moving the notches makes the data signals more difficult to detect audibly.
Other prior art uses a combination of phase, time and frequency domains to impart digital information on lossy and lossless carrier data. In U.S. Pat. No. 5,940,135 to Petrovic et al. (1999), an encoder employs the preprocessing of a slowly varying phase distortion coupled with a complex echo hiding system, involving multiple time-varying echoes to instill a digital watermark on a pre-recorded carrier.
Digital watermarks are effective in applications such as digital rights management for compact discs (CDs) and digital video discs (DVDs) where the attribution of the watermarked carrier is permanently identified with a single source such as a studio, publisher or performing artist, and multiple copies of the carrier are to be distributed. The digital watermark fails in efficacy where the identification, verification or authentication must be attributed to multiple sources such as the purchasers of broadcast radio or television advertising time that are not associated with the producer of the digital watermarked advertising content provided to the broadcaster. Digital watermarking systems for audio carriers such as U.S. Pat. No. 5,940,135 to Petrovic et al. (1999) generally employ techniques that in some way manipulate the carrier in either the phase, time or frequency domains, or any number of permutations of the three. These approaches appear to the accomplished listener as audible degradations of the audio carrier.
Other known identification injecting methods use frequency spread spectrum techniques to periodically inject time-stamp and identification information into master audio recordings for the purpose of recovering this time and identification data for performance verification. U.S. Pat. No. 5,379,345 to Greenberg (1995) is one such example. This approach, like digital watermarking, while effective in identifying mass copies of advertising content, fails in efficacy where the encoded identification points to an individual or entity other than the purchaser of the radio or television broadcast advertising time seeking proof of performance.
Another instance of the use of frequency spread spectrum techniques coupled with encryption that also injects a time stamp and identification information is U.S. patent application Ser. No. 09/915,174 to Nash-Putnam (2001). This approach, like Greenberg above, injects the identifier specifically in real-time and at the time of transmission. The approach suffers from a failing, which is typical of frequency spread spectrum techniques, in that the frequency spreading appears as noise in the audio carrier. In the absence of audio data carrier components to mask the code frequencies, they can become audible. This method, therefore, relies on the asserted noise-like character of the codes to suggest that their presence will be ignored by listeners. However, in the case of an accomplished listener this assumption may not be valid, for example, in the case of recorded music containing passages with relatively little audio carrier content or during pauses in speech.
Other forms of identification, verification, and authentication rely on digital fingerprinting or other related pattern recognition techniques. These approaches require prior knowledge of the subject carrier, which are not available in real-time. Also, such comparison techniques are of only limited reliability due to normal degradation of the signal due to airborne broadcast transmission, such as electromagnetic interference, multi-path transmission errors, and a number of other environmental disturbances. These forms of pattern comparison of a portion of an audio carrier can be utilized for identification purposes, but the comparison requires significant analysis and has a high probability of inaccuracy.
Still other prior art techniques employ the psychoacoustic model of the human perception characteristic, more specifically temporal masking, to insert modulated or unmodulated tones into carrier data such that they will be masked by existing frequency components, and thus not perceived, e.g. U.S. Pat. No. 5,319,735 to Preuss et al. (1994) and U.S. Pat. No. 5,450,490 to Jensen et al. (1998). Such techniques are expensive and complicated to implement, while suffering from a susceptibility to degradation in the face of environmental signal distortions or distortions imposed by perception-based compression schemes designed to eliminate masked signal components.
The prior art fails to provide a relatively simple system and method for the insertion and retrieval of identifying artifacts in lossy or lossless carriers. The prior art also fails to provide systems and methods for the continuous, real-time insertion and retrieval of digital artifacts in lossy and lossless carrier data sequences that produces humanly perceived audio transmissions with inaudible artifacts defining digital information.